We present the petrographic and structural features of the Precambrian (Neoproterozoic) Basement rocks of the Benin-Nigerian Shield that crop out in Northwestern Nigeria within Kanoma and its environs to give an insight on the evolution and deformational episodes that pervaded them. The major rock types in the area are schists and quartzites which have been intruded by granitic rocks. The origin of these rocks can be attributed to the Eburnean-Kibaran Precambrian orogenic episodes and the Pan-African orogeny which started and ended with the intrusion of the granite suites. The dominant mineralogy associated with the rock types includes quartz, orthoclase, plagioclase, microcline, and biotite and very little accessory minerals. Structural features such as joints, quartz veins with minor folds and faults observed in the lithological units have a predominant N-S trend and are the imprints of the last tectonic event (Pan-African orogeny). The level of deformation in Kanoma led to the development of N to NNE trending moderately (S1) to steeply (S2) dipping foliations in the schist. The evolution of these deformational mechanisms from moderately dipping foliations to steeply dipping foliations along the N to NNE- trend is associated with late orogenic uplift and exhumation following oblique convergence during the Pan-African orogeny. Structural overprinting relations recognized within Kanoma and its environs allow us to decipher the geologic structures into three successive Pan-African deformational events (D1â€“D3). D1 fabrics are manifested by simple anticline micro folds in the schist. The D2 structures are the predominant ones in the area comprising the N-S directional joints and faults. The D3 phase of deformation is a progressive one which started as N-S high angle thrusts and thrust-related folds that resulted from the NEâ€“SW contraction during the orogenic episodes. The studied rocks can be correlated with the Pan-African and Brasiliano belts based on overlapping features.
Keywords: Petrography, structural evolution, Precambrian basement rocks, Benin-Nigerian Shield, Kanoma, Nigeria